Years with Boston: 1915-1922, 1934 (62-59, 3.67 ERA, 358 strikeouts, 299 walks, 1,089.1 innings)
Best Year in Boston: 1919 (16-8, 2.71 ERA, 70 strikeouts, 48 walks, 219 innings)
Pennock returned to Boston in 1919 and became one of Boston's most consistent starters on an otherwise underwhelming rotation. Boston had already lost Carl Mays, Ernie Shore, and Dutch Leonard, and Babe Ruth became an outfielder. Pennock lead the team in victories that season as well as in 1920 with 16 in both seasons. Pennock continued to be a good pitcher throughout his first tenure in Boston, but it was not until he was traded to the Yankees that he became a big star.
The Red Sox traded Pennock to the Yankees for Norm McMillan, George Murray, and Camp Skinner. None of whom did anything of substance. They also received $50,000.00. With the Yankees, Pennock was able to pitch for a good team again and his record improved. He was one of the big pitching stars for the 1920's dynasty Yankees.
In 1934, Pennock returned to the Red Sox. He was 40, but still had a decent season, mostly as a reliever. He was 2-0 with a 3.05 ERA.
Pennock is wearing a Red Sox cap on his Hall of Fame plaque (I am sure of it), but most of his best years were spent with the Yankees.